Radio-opaque tooth post made of composite material

ABSTRACT

A tooth post made of composite material includes a central core (3) made of a resin matrix wherein are embedded fibers (5) which give the post (1) its main mechanical properties. The central core (3) is wrapped in a sheath (6) consisting of at least one layer of fiber (7) made of radio-opaque material.

The present invention relates to a tooth post made of composite materialpresenting an opacity allowing easy location thereof by radiography.

It is known that, in the dental art, in order to strengthen a tooth,posts are employed which are mostly made of metal. Although these postsare easily locatable by the conventional means of radiography, theynonetheless present the drawback of presenting moduli of elasticity verydifferent from those of the teeth in which they are fixed, so that theytend, during use, to injure the dentin, thus bringing about theirrelease after a more or less long time.

In order to avoid this drawback, it has been proposed to employ postsmade of composite materials of which the moduli of elasticity are closeto those of the dentin, so that they preserve the latter, consequentlyensuring a long-lasting hold of the post.

Such posts are mostly constituted by elements transparent to X-rays, sothat they are difficult to locate, which is deterimental, on the onehand, from the medical standpoint, particularly in the case of anaccidental ingestion, and on the other hand, from the administrativestandpoint if it is desired to prove that these posts have beenpositioned.

It is, of course, possible, in order to ensure opacity of a post, toincorporate in the resin of which it is constituted, radio-opaquefillers which one attempts to distribute regularly in its mass. Now, ithas been ascertained that, even when these fillers were relatively welldistributed, the contour of the post obtained in X-radiography was notperfectly defined, particularly when the outer face of the post hadundergone a specific machining. In order to avoid this drawback, asolution would be to increase the quantity of the fillers used. However,it has been ascertained that, in order to obtain a post whose contourunder X radiography is perfectly defined, it was necessary to add aquantity of fillers such that the mechanical qualities of the post werethen reduced.

It is an object of the present invention to propose a means for making atooth post whose contour, obtained under X-radiography, is perfectlydefined without its mechanical qualities being reduced.

The present invention thus has for its object a tooth post made ofcomposite material, characterized in that it comprises a central coreconstituted by a matrix of hardenable resin in which are embedded fiberswhich give the post its main mechanical qualities, this central corebeing surrounded by a sheath constituted by at least one layer of fibersmade of a radio-opaque material.

The fibers constituting the sheath may preferably be constituted bycontinuous fibers which extend substantially from one end of the post tothe other. Furthermore, the fibers of the central core may beconstituted by fibers transparent to X-rays.

In one embodiment of the invention, the peripheral sheath is constitutedby at least two layers of intersecting fibers.

The fibers constituting the peripheral sheath are advantageously fibersof silica, ceramics, silicon carbide, or glass fibers with a highcontent of calcium oxide.

An embodiment of the present invention will be described hereinafter byway of non-limiting example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a view in axial and longitudinal section of a post accordingto the invention.

FIG. 2 is an enlarged partial view in elevation of the post shown inFIG. 1.

FIG. 3 is an enlarged partial view in elevation of a variant embodimentof a post according to the invention.

FIGS. 1 and 2 show a tooth post 1 comprising a central core 3 formed bya matrix of epoxy resin in which are embedded fibers transparent toX-rays such as glass fibers 5 which extend over the whole length of thepost 1. The nature of these fibers, their diameter and their quality aredetermined by the mechanical qualities that it is desired to give thepost 1.

The periphery of the post comprises a sheath 6 formed by a layer ofradio-opaque fibers 7 which are disposed longitudinally over the wholelength of the post 1.

These fibers 7 are preferably isotropic fibers, which enables them tomodify only slightly by their presence the transverse and longitudinalmoduli of elasticity given to the post 1 by the core 3 thereof.Preferably, and for the same reason, the modulus of elasticity of thesefibers 7 is as low as possible. As for their refractive index, it is ashigh as possible. The thickness of the peripheral sheath 6 extends overone or more layers and is particularly small having regard to theoverall thickness of the post 1.

In order to constitute the sheath 6, ceramic fibers may thus beemployed, which have isotropic properties and of which the longitudinaland transverse moduli of elasticity are of the order of 186 GPa and ofwhich the refractive index is of the order of 1.62.

Silicon carbide fibers may also be employed, whose modulus of elasticityis close to that of the ceramic fibers, but which present a refractiveindex greater than 2. Such fibers can be used in a lesser quantity, forequal opacity, which makes it possible to minimize their influence onthe transverse and longitudinal moduli of elasticity of the post 1.

It has been ascertained that the dental post in accordance with theinvention presented on the X-radiographies a perfectly defined contour,which, on the one hand, enabled their precise positioning with respectto the tooth to be defined, but also their specific shape to be defined.

The fibers 7 constituting the peripheral sheath 6 may be contiguous, butit is, of course, possible, according to the invention, to constitute aperipheral sheath by means of non-contiguous fibers possibly coming intocontact with one another at points.

In an embodiment of the invention shown in FIG. 3, the peripheral sheath6 is thus constituted by two superposed and intersecting layers offibers 7 and 7', which are helically wound on the periphery of thepost 1. Such an arrangement makes it possible to obtain a regulardistribution over the whole outer surface of the post, of points ofgreater opacity corresponding to the points of intersection A of fibers7 and 7'. The regular distribution obtained on the periphery of the post1 makes it possible clearly to define the radiographic contour thereof.

According to the invention, the central elements constituting the coreof the post 1 and in particular the nature, quantity and distribution ofthe fibers, are used to give the post the desired mechanical qualitiesand in particular the longitudinal and transverse moduli of elasticity.The radio-opaque fibers disposed on the periphery may be such that theyhave the least possible influence on the mechanical characteristics ofthe post, so that their sole role is to control the radio-opacity of thepost.

In order to constitute the sheath 6, glass fibers with a high rate ofcalcium oxide, of the order of 17% to 25% by weight, may also be used,such as those marketed by the firm OWENS CORNING FIBERGLASS under theTrademark "ECR GLASS".

These fibers present the advantage of possessing a high refractiveindex, of the order of 1.58, as well as an excellent corrosionresistance. These fibers, while moreover using high-resistance glassfibers to constitute the central core, make it possible to produce adental post of great homogeneity.

Furthermore, by reason of their colour, these fibers are particularlyinteresting from the aesthetic standpoint.

We claim:
 1. Tooth post made of composite material, characterized inthat it comprises a central core (3) constituted by a matrix ofhardenable resin in which are embedded fibers (5) which give the post(1) its main mechanical qualities, this central core (3) beingsurrounded by a sheath (6) constituted by at least one layer of fibers(7) made of a radio-opaque material.
 2. The post according to claim 1,characterized in that the sheath is constituted by continuous fiberswhich extend substantially from one end of the post to the other.
 3. Thepost according to claim 1, characterized in that the fibers of thecentral core are transparent to X-rays.
 4. The post according to claim1, characterized in that the peripheral sheath (6) is constituted by atleast two intersecting layers of fibers (7).
 5. The post according toclaim 1, characterized in that the peripheral sheath (6) is constitutedby at least one layer of fibers oriented in the same direction as thecentral fibers.
 6. The post according to claim 1, characterized in thatthe fibers constituting the peripheral sheath (6) are silicon carbidefibers.
 7. The post according to claim 1, characterized in that thefibers constituting the peripheral sheath (6) are silica fibers.
 8. Thepost according to claim 1, characterized in that the fibers constitutingthe peripheral sheath (6) are ceramic fibers.
 9. The post according toclaim 1, characterized in that the fibers constituting the peripheralsheath (6) are glass fibers with a high proportion of calcium oxide. 10.The post according to claim 9, characterized in that the glass fiberscontain between 15% and 30% by weight of calcium oxide.